A plastic substrate of polycarbonate, polyethylene terephthalate and the like has been investigated as a substrate of a flexible display device such as an electronic paper. However, these plastic substrates have the problem of causing slight extension and shrinkage during being heated, and accordingly have been required to have higher heat resistance. On the other hand, an organic thin film transistor has received attention as a transistor to be mounted on the above-described substrate of the device, because of being a thin type and superior in flexibility. Because the plastic substrate has not had sufficient heat resistance as was described above, a process of manufacturing an organic thin film transistor on a substrate can be preferably conducted at as low a temperature as possible.
In the process of manufacturing the organic thin film transistor, generally, a process of film-forming/curing a gate insulating film which is an insulating layer provided between a gate electrode and an organic semiconductor layer has been particularly required to be conducted at a high temperature. Accordingly, in order to conduct the process of manufacturing the organic thin film transistor at a low temperature, it is important to conduct a step of forming the gate insulating film at a low temperature.
A method of anodizing the surface of a gate electrode (see Patent Literature 1), a method of forming the film with a chemical vapor deposition method (see Patent Literature 2) and the like are known as the method for forming the gate insulating film at a low temperature. However, in these methods, the process of forming the gate insulating film is complicated.
For this reason, it is investigated as means for simply forming the gate insulating film at a low temperature to form the film with the means of application or the like. For instance, the following Non Patent Literature 1 describes a method of forming the gate insulating film by spin-coating poly(4-vinylphenol) or poly(melamine-formaldehyde), and curing the compound at 200° C.